Rapid prototyping is defined as computer-controlled additive fabrication, in that an object can be fabricated by the addition of material rather than conventional machining methods that rely on removal or the subtraction of material. The term “rapid” is, it will be appreciated, a relative term but one that has specific meaning within the art, in that construction of a finished three dimensional article can take from several hours to several days, depending on the method used and the size and complexity of the model. There are many known methodologies that are employed within the general field of rapid prototyping Layered Object Manufacture (LOM) is one form of Rapid prototyping (RP) which relates to the successive layering of adhesive-coated paper, plastic, or metal laminates which are then successively glued together and cut to shape with a knife or laser cutter.
LOM, similarly to other rapid prototyping techniques, conventionally involves the use of a three dimensional (3D) computer aided design (CAD) of an object/part to be made, from which a stereolithography (STL) or other suitable format file is generated within a CAD package. The STL file is processed and in effect virtually sliced in the Z-axis at a thickness matching the thickness of the substrate material used. This creates a series of cross sections of the part and at any particular height each one has a simple two dimensional (2D) profile. A profiling, or cutting, apparatus may be used to trace the 2D profiles and thus cut the shapes onto thin sheets of raw material. In LOM, each individual thin sheet may be stacked and bonded one on top of another to produce a finished 3D object. After a plurality of media object layers are formed, a profiling and layer bonding process is performed. The plurality of layers are bonded together, and then a profiling or weeding process is performed which comprises removing unwanted support material from the printed media stack to reveal the 3D printed object. The order of the profiling, stacking and bonding processes may be interchanged. The individual layers may also be printed using conventional 2D printing processes. The layers may be singly or duplex printed, and printed either in a single colour such as with black ink, or colour printed with a plurality of colours. In addition multi-coloured paper may be used.
In LOM manufacturing, typically a finished 3D object is formed from a stack of individual media layers which are assembled and profiled to form the desired final geometrical shape. The individual media layers may be printed or otherwise treated prior to the assembly arrangement. Accordingly, a plurality of 3D object media layers may be printed in preparation for forming the finished 3D printed article. The entire layer stack for the 3D printed article may be pre-printed off-line in the printing module, after which the printed stack may be loaded into the profiling and layer bonding module where each printed layer may be profiled and bonded to complete the fabrication of the 3D printed article.
Problems may arise in terms of alignment of the images printed on the opposite sides of the printed media layers in preparation for the collation and assembly into the final 3D object. Problems may also arise if the printed sheets provided as input to a 3-D printer are not in the correct order.
Some printers can be used to manufacture parts in colour. In one approach, for example, coloured sheets may be used. In another approach, for example, a coloured ink may be printed onto each sheet of paper or an image may be printed onto each sheet and the printed sheets may then be loaded into the section of the printer where the cutting and gluing occurs.
It will be appreciated that use of coloured sheets and/or inks and printing of images may add further complexity to the 3D printer machine and/or processes.
Considerations in choosing a 3D printing machine include speed, cost of the 3D printer, cost of the printed prototype, and cost and choice of materials and colour capabilities. Often the cost of 3D printing is too high to be practical for most consumer applications. Furthermore, often currently available 3D printers are too large for consumer application.
The use of paper in SDL has brought down the cost of raw materials, but the size and complexity of printers remains and there is a need to develop more compact and less complex printers, which can be produced more cheaply and fit on a consumer's home desktop.
There are therefore a number of issues with 3D printing processes and systems for rapid prototyping that need to be addressed. The present application is aimed at providing an improved method of manufacturing coloured objects. The present specification is aimed also at providing and improved 3D printing system.